Session: 09-02-06 Wind Energy: Dynamic Analysis II

Submission Number: 181943

Comparison of Towing Performance Between Two Semi-Submersible Floating Offshore Wind Turbine Under Head-Sea Conditions 

This study investigated the wet-towing performance at various speeds of two semi-submersible floating offshore wind turbine (FOWT) platforms, i.e., barge and column types, under head-sea conditions. Although FOWTs provide hydrodynamic advantages over fixed-bottom wind turbines, their wet-towing phase presented significant engineering challenges. To address these, a numerical simulation framework was implemented in OrcaFlex to model the 6-DOF motions of a 13.2 MW semi-submersible FOWT during wet-towing. The model accounted for the platform’s inertial and restoring forces, as well as external loads including aerodynamic thrust from the turbine, hydrodynamic drag induced by wind and currents, wave excitation forces, and dynamic towline tensions. Hydrodynamic coefficients were obtained using ANSYS AQWA based on potential flow theory and refined with viscous effects using STAR-CCM+. Aerodynamic forces were modelled using blade element momentum theory (BEM), while towline tensions were analyzed using the finite element method (FEM). Irregular sea states were simulated with the JONSWAP spectrum, employing a peak enhancement factor tuned to regional wave characteristics in the target offshore area. The towing configuration involved three tugboats pulling the FOWT at speeds ranging from 1 knot to 3 knots using steel wire ropes connected at designated fairlead points. Key performance indicators, e.g., nacelle acceleration, platform tilt angle and towline tension, were evaluated across this speed range. The results indicated that the column-type platform demonstrated a more favorable balance of safety and operational reliability, maintaining all key parameters within design limits, i.e., 4.91m/s² and 5°, and exhibiting moderate towline tension distribution. In contrast, the barge-type platform exhibited superior tension performance with lower average values, while nacelle acceleration approaching the allowable limit under head-sea conditions.

Presenting Author: Min-Ju Tsai Department of Engineering Science and Ocean Engineering

Presenting Author Biography: Min-Ju Tsai is the presenting author. He is a master's student in Department of Engineering Science and Ocean Engineering at National Taiwan University, conducting his research on offshore wind technology under the supervision of Professor Shiu-Wu Chau.

Authors:

Min-Ju Tsai Department of Engineering Science and Ocean Engineering
Shiu-Wu Chau Department of Engineering Science and Ocean Engineering